Mie理论在静态光散射粒度测量的应用下限研究

测量下限是光散射颗粒测试技术的关键问题。本文通过理论分析、比较归一化散射光强的分布图和构造方差函数F(d)对颗粒散射光的光强分布进行了定性和定量的讨论,对Mie散射向Rayleigh散射趋近的情况进行了分析,讨论了散射光光强大小的分布,分析了测量不同粒径的颗粒的可行性,最终得到在入射光源是波长为0.6328μm的He-Ne激光器的情况下,当粒径d取200nm以上时,不同粒径颗粒的M ie散射光强分布有较大差别,适合用静态光散射的方法来判断颗粒粒径。     

火灾烟雾颗粒的光学散射特性研究

从理论和实验两个方面研究了几种常见的燃烧烟雾在不同波长激光下的散射特性。从Mie散射理论出发，比较几种Mie散射算法的优缺点，采用一种改进的连分式算法对火灾烟雾颗粒的散射光强分布进行计算，得出不同粒径大小和波长下光强分布图。结合理论计算，设计一套实验装置，测量并计算在不同角度下3种烟雾颗粒和面粉气溶胶散射光的相对光强比，实验测量值与理论计算值吻合较好。研究结果表明不同种类烟雾散射光相对光强比互不相同，火灾烟雾与非烟雾气溶胶差距较大，从而表明散射光相对光强比是区分不同烟雾特定的物性参数，为火灾烟雾探测技术发     

纳米及微米磁性颗粒在长波长下的光散射特性分析

根据Mie散射理论,分析计算了纳米级、微米级磁性颗粒的光散射特性。针对目前在导航、遥控及雷达等行业广泛应用的纳米、微米磁性颗粒,在Mie散射系数中引入磁导率变量,对比分析了磁性与非磁性颗粒、吸收性与非吸收性颗粒的散射特性规律。数值计算结果表明,磁导率的变化对具有吸收性磁性颗粒的散射特性造成影响,随着磁导率的增大,颗粒的散射光强及吸收性能将逐渐增大,同时磁导率增大对颗粒散射特性的影响将会受到复折射率实部的制约。     

粗糙表面镜向散射光强统计

粗糙表面散射可分为镜向散射和非镜向散射,镜向散射光强的分析不仅具有理论上的简洁性,而且能够给出粗糙表面散射的一些重要特性.论文根据相干散射和傅里叶光学理论,对粗糙表面的镜向散射光场进行了理论分析和推导,结果表明:镜向散射光场的主要特征由粗糙表面高度分布的傅里叶变换和入射光场的傅里叶变换共同决定.对于均匀平行光照射高斯表...     

亚微米级扁椭球颗粒群的散射特性

采用T矩阵方法计算亚微米级扁椭球随机取向分布颗粒群的散射特性,研究消光截面、散射截面、吸光截面、单散射反照率、非对称因子以及散射矩阵元素与颗粒的大小、折射率、长短轴比之间的关系。结果表明,随颗粒粒径增大,消光截面、散射截面、吸光截面、非对称因子都单调增加,散射相函数F11的角分布曲线特征可以区分颗粒的大小;颗粒越偏离球形,颗粒对入射光的衰减效率越低,后向散射光强越强,在轴比不大时,前向50°内的F22/F11值可以区分颗粒的形状;折射率变化主要是对后向散射光的分布产生影响,实部、虚部的变化可分别通过F34/F11的角分布曲线、F12/F11的第一个峰值来体现。     

X射线散射光子对剂量当量电离室影响

为了测量X射线辐射散射光子对剂量当量电离室的影响,根据ISO-4037建立X射线防护水平参考辐射场.采用PTW-32002 1L和PTW-32003 10L两个不同体积的球形空腔电离室在不同辐射质条件下通过影锥屏蔽法测量散射光子对不同电离室的影响程度.实验结果表明:散射光子对不同体积电离室影响程度不同,对于10 L球形电离室散射份额在2％左右,而对于1L球形电离室散射份额在4％左右.能量越高,散射光子的散射份额也会相对增大.     

颗粒层状结构对散射特性及激光粒度测量的影响

根据Aden-Kerker理论,对双层颗粒前向散射特性进行了研究。在此基础上,分别用衍射理论、Mie理论和Aden-Kerker理论计算了散射系数矩阵并采用非独立模式算法进行反演。数值计算结果表明,双层颗粒的散射光强由颗粒折射率和内外径决定,在实际的激光前向散射粒度测量中,如果沿用Fraunhofer衍射理论或Mie理论计算系数矩阵,在测量双层颗粒时,反演结果会有一定的误差。相比于Mie理论,衍射理论的反演误差更大。     

Rise-2008型激光粒度仪／粒度分析仪

Rism2008型激光粒度分析仪采用全量程米氏散射理论,充分考虑到被测颗粒和分散介质的折射率等光学性质,根据大小不同的颗粒在各角度上散射光强的变化反演出颗粒群的粒度分布数据。     

球形壳体障板声散射近场矢量特性

为了实现矢量水听器在水面或水下载体上的工程应用,研究了球形壳体障板声散射近场矢量特性。采用弹性薄壳理论结合边界条件导出了球形壳体障板声散射的声压和质点振速表达式,给出相应的声强表达式。数值计算了球形壳体障板声散射的近场特性,重点关注其近场矢量特性。理论分析和数值计算结果表明,由于球形壳体障板的散射作用,声压场和质点振速场表现为复杂的干涉结构;质点振速方向和声源方位不一致;声压和质点振速不再同相;声强方向也不再反映声源方位。本文结果为矢量水听器在球形载体和球形障板条件下的工程应用提供理论依据。     

Rise-2008型激光粒度仪／粒度分析仪

工作原理： Rise-2008型激光粒度分析仪采用全量程米氏散射理论，充分考虑到被测颗粒和分散介质的折射率等光学性质，根据大小不同的颗粒在各角度上散射光强的变化反演出颗粒群的粒度分布数据。     

降低超细高氯酸铵感度的方法研究

为了降低超细高氯酸铵(AP)的机械感度,以十八烷胺为包覆剂,经气流粉碎工艺,制备了超细AP包覆粒子。通过对超细AP包覆粒子进行粒度分析、SEM分析、DSC分析及感度检测,研究了超细AP包覆粒子的包覆效果、热分解特性及感度特性。试验结果表明:超细AP包覆粒子,粒度为D50=5.8μm,表面有包覆层存在;超细AP包覆粒子的感度,与超细AP样品相比,当包覆剂质量分数为1%时,撞击感度降低31.2%,摩擦感度降低12.0%;当包覆剂质量分数为3%时,撞击感度降低34.5%,摩擦感度降低22.0%,且包覆剂用量越大,撞击感度和摩擦感度越低;但包覆剂对AP的热分解会产生一定的负面影响,质量分数应≤1%。     

Light scattering simulation by oblate disc spheres using the null field method with discrete sources located in the complex plane

The T-matrix method, which is also known as the null field method (NFM) or extended boundary condition method (EBCM), has established itself as a well known and highly regarded method for calculating light scattering by non-spherical particles. Its biggest advantage is the possibility to obtain all information about the scattering characteristics of the particle and to store it into one matrix. This enables one to do additional investigations with low efforts. Unfortunately the standard NFM fails to converge for particles with extremely non-spherical particle shapes, like long cylinders or coin-like flat cylinders. In this paper we investigate light scattering by finite particles in the form of an oblate disc sphere, which can be described as flat cylinders with a rounded edge. We use an advanced form of the T-matrix method—the null field method with discrete sources (NFM-DS). By presenting light scattering results we would like to demonstrate the potential this advanced NFM-DS offers. It allows one to calculate particle shapes with aspect ratios (relation between radius and thickness of the particle) up to 100:1 and size parameters (relation between radius and wavelength) up to 30.     

Intrinsic aberrations due to Mie scattering in particle holography

Holography of small particles is a newly revived topic because of its importance in holographic particle image velocimetry (HPIV). However, the property of particle images formed through holography remains largely unexplored. This fact undermines the measurement reliability of HPIV techniques and has become one of the obstacles in the full deployment of HPIV. We study the intrinsic aberrations in the holographic particle image introduced by particle light scattering and investigate how accurately holography can deliver information about the particles that are being imaged. Consistent with our experimental observations, simulations based on Mie scattering theory show that even with a perfect hologram the reconstructed particle images demonstrate complex three-dimensional morphologies and bodily shifts. These characteristics, manifested as image aberrations, result from uneven scattering amplitude and phase distributions across the finite aperture of the hologram. Such aberrations degrade the signal-to-noise ratio in the reconstructed image as well as introducing systematic errors in detected particle image positions. We examine the effect of these aberrations on HPIV measurements.     

Light scattering by an infinite circular cylinder immersed in an absorbing medium

Analytic solutions are developed for the single-scattering properties of an infinite dielectric cylinder embedded in an absorbing medium with normal incidence, which include extinction, scattering and absorption efficiencies, the scattering phase function, and the asymmetry factor. The extinction and scattering efficiencies are derived by the near-field solutions at the surface of the particle. The normalized scattering phase function is obtained by use of the far-field approximation. Computational results show that, although the absorbing medium significantly reduces the scattering efficiency, it has little effect on absorption efficiency. The absorbing medium can significantly change the conventional phase function. The absorbing medium also strongly affects the polarization of the scattered light. However, for large absorbing particles the degrees of polarization change little with the medium's absorption. This implies that, if the transmitting lights are strongly weakened inside the particle, the scattered polarized lights can be used to identify objects even when the absorption property of the host medium is unknown, which is important for both active and passive remote sensing.     

人造水雾粒度测试及红外消光因子计算分析

在大型半密闭空间内发生具有不同粒度分布的水雾体系,用喷雾激光粒度仪测试粒度分布规律并采用Van Der Hulst公式计算不同大小水雾粒子对红外辐射的散射效率因子、吸收效率因子和消光效率因子。结果表明:试验条件下水雾粒子的平均直径在5~65μm范围内。计算结果显示:水雾粒子对3～5、8～14μm红外辐射的消光作用主要取决于散射效应而非吸收效应。当水雾粒子的直径大于等于红外辐射的波长时,水雾体系对该波长红外辐射能够产生较强的消光效果。综合分析水雾体系的稳定性和消光特性,直径在3~30μm之间的水雾粒子对3～5、8～14μm红外辐射的衰减效果更为明显。     

石墨气溶胶粒度分布及远红外消光因子研究

在烟幕试验箱中测试了不同湿度条件下超细石墨气溶胶的粒子分布及其随时间变化的规律。根据Mie散射理论计算了石墨气溶胶粒子对8～14μm远红外的消光因子。分析表明,石墨气溶胶的粒度随着分散时间延长和空气相对湿度减小而变小。小尺度的石墨气溶胶粒子对8～14μm红外的消光效率因子非常小,但随着气溶胶粒子直径的增加,消光效率因子显著变大并趋于稳定。直径大于2.5μm的石墨气溶胶粒子均能够对8～14μm远红外产生良好的消光效果。     

多角度动态光散射法的纳米颗粒精确测量

基于动态光散射原理,采用自主研发的多角度动态光散射装置,对纳米及亚微米颗粒粒径准确测量方法进行了探究。自研装置采用带有光阑组的精密入射光路设计,以及匹配液池及Beam-stop设计,极大提高了信噪比;同时避免了测量角度的互补方向上,由于样品池与空气界面折射率不同导致的反射光信号对有效信号的干扰。在此基础上,对不同浓度、粒径的聚苯乙烯(PS)颗粒溶液进行了测定及不确定度分析。结果表明,对同一粒径的PS颗粒,增加颗粒浓度时,多重散射首先发生于大、小测量角度,越接近90°,发生多重散射的浓度越高;随着粒径增大,受不可忽略的颗粒间相互作用的影响,粒径测量结果表现出了强烈的角度依赖性,甚至波动性。     

Orientation dependence in near-field scattering from TiO(2) particles

This scattering of light by small particles embedded in a continuous transparent medium is influenced not only by the bulk optical properties of the particles and the medium but also by the size, shape, and spatial arrangement of the particles-that is, by the microstructure. If the particles are close together, as in agglomerated coatings or stereolithographic suspensions, interactions between the radiation fields of adjacent particles can lead to variations in the magnitude and spatial arrangement of the scattered light in the near and the far field, which can affect the color and hiding power of a coating, the cure depth and homogeneity in stereolithography, and the threshold intensity for stimulated emission in random lasers. Our calculations of the near- and the far-field scattering distribution for 200-nm TiO(2) spheres in pairs of various orientations and in an ordered array of five particles show that, depending on the orientation of the particles with respect to the incident light, these interactions can either increase or decrease the scattering efficiency, the isotropy of the scattering, and the magnitude of the electric field strength within the matrix and the particles. In the mid-visible range, two particles in line increase the backscattering fraction by 28% and the scattering strength by 38% over that of a single particle, whereas if the particles are in the diagonal configuration the backscattering fraction and scattering strength are actually reduced by addition of the second particle. At shorter or longer wavelengths the backscattering fraction is reduced regardless of the location of the second particle, by as much as 60% when five particles are arranged in the zigzag configuration. These results are surprising in that it is generally assumed that multiple scattering enhances backscattering. Simple models of multiple scattering or scattering of two particles as a single, larger particle are inadequate to explain these results.